linux-kernel - Re: [PATCH v3] driver core: Move device_links_purge() after bus_remove

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Date:   Fri, 20 Oct 2017 13:17:35 +0200
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Jeffy Chen <jeffy.chen@...k-chips.com>,
        linux-kernel@...r.kernel.org, briannorris@...omium.org,
        heiko@...ech.de, dmitry.torokhov@...il.com, dianders@...omium.org,
        tfiga@...omium.org, broonie@...nel.org, seanpaul@...omium.org,
        thierry.reding@...il.com
Subject: Re: [PATCH v3] driver core: Move device_links_purge() after bus_remove_device()

On Friday, October 20, 2017 8:22:01 AM CEST Greg KH wrote:
> On Fri, Oct 20, 2017 at 03:22:07AM +0200, Rafael J. Wysocki wrote:
> > On Friday, October 20, 2017 3:23:16 AM CEST Jeffy Chen wrote:
> > > The current ordering of code in device_del() triggers a WARN_ON()
> > > in device_links_purge(), because of an unexpected link status.
> > > 
> > > The device_links_unbind_consumers() call in device_release_driver()
> > > has to take place before device_links_purge() for the status of all
> > > links to be correct, so move the device_links_purge() call in
> > > device_del() after the invocation of bus_remove_device() which calls
> > > device_release_driver().
> > > 
> > > Signed-off-by: Jeffy Chen <jeffy.chen@...k-chips.com>
> > > Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> > 
> > OK, thanks.
> > 
> > Greg, will you take this?
> 
> Yes I will.  But I don't understand if this is a bugfix that needs to go
> to all stable kernels to resolve a problem that has always been there,
> or it is ok for 4.15-rc1, as it's just a "do things in the correct
> order" type of change.
> 
> Any hints?

Technically the problem has always been there, but it is only visible if
device links are used in a specific way and I'm not sure whether or not
there is any code in the tree where that's the case.

That said AFAICS it should be safe to add

Fixes: 9ed9895370ae (driver core: Functional dependencies tracking support)

to it and handle it accordingly.

Thanks,
Rafael